It's no surprise that, as Mexico's presidency changed hands, commentary on both sides of the border focused on the drug war. During the previous administration, cartel-related killings had more than doubled, despite government crackdowns. The incoming president, promising to make his country safer, announced a controversial new approach. The year? 2006.

That's right: Felipe Calderon's "war," declared only weeks into his presidency, was intended to crush the cartels and reverse the deteriorating security situation. Instead, it unleashed an eightfold increase in killings - 60,000 so far - that not even his harshest critics predicted, devastating proof of how poorly we understand drug-war dynamics.

Leaving office in 2012, Calderon sought to lock in his "no quarter" approach; the cartels, he argues, are in their death throes. But newly inaugurated Mexican President Enrique Peña Nieto and his Institutional Revolutionary Party (the once all-powerful and highly corrupt PRI) see a crucial opportunity to recalibrate Mexico's drug policy. Amid the maelstrom of drug-related violence that still racks Mexico, and the overfilling of prisons in the U.S. with drug offenders, such change is welcome.

At face value, Peña Nieto describes a sensible middle path: continuing U.S.-Mexico cooperation and expanding law-enforcement capacity while emphasizing violence-reduction over drug interdiction. Like President Obama's comments on marijuana legalization in Oregon and Colorado, Peña Nieto's leave room to maneuver. Both leaders, though, seem to be reaching for reasonable re-orderings of law-enforcement priorities.

Yet America's drug warriors bristle at any suggestion of reform. Rep. Jim Sensenbrenner, R-Wis., publicly worried about a "reversion" to the corrupt pact of the PRI's heyday, when it "minimized violence by turning a blind eye to the cartels." Former Drug Enforcement Administration Director Robert C. Bonner portrayed a stark, epochal choice: "Accommodation may reduce some of the violence in the short run, but in the end, the only way for Mexico to restore order is to defeat the cartels once and for all."

This view is seductive - and misleading.

Calderon's crackdown - designed to fragment Mexico's mega-cartels into smaller groups with less firepower - succeeded in splintering them, but fighting only intensified. Kingpins were eliminated, but this created new opportunities for upstarts. Above all, the drugs keep flowing.

Even if bloodshed in Mexico were somehow an acceptable price to pay for keeping cocaine out of the U.S., years of extreme violence have only bought, at best, a moderate decrease in drug availability (measured by increases in U.S. street prices). Indeed, since 2009, killings in Mexico have spiked, while U.S. street prices fell. Calderon himself now says that ending the drug trade is "impossible."

The idea that Mexico must choose between crackdowns and corruption also rests on misconceptions. In fact, crackdowns give cartels more incentives to buy off top officials: Witness the recent arrest of Mexican army generals for taking multimillion-dollar bribes and the spate of corruption charges against U.S. border agents.

My research suggests that when crackdowns push up the price of bribes, cartels respond with more violence and intimidation - their way of forcing prices back down. This explains how the "successes" of Calderon's war - 23 drug kingpins captured or killed, 11,000 tons of drugs seized, etc. - can coexist alongside an upsurge in both antistate violence and corruption scandals.

The flip side is that reducing violence need not imply surrender or systematic corruption. On the contrary, Mexico needs to use all its leverage - here's where stronger federal police and U.S.-supplied equipment and know-how come in - to punish cartels for their violent acts. Traffickers need to know that the more violently they deal drugs, the more aggressively the state will pursue them.

This requires, by definition, going relatively easier on nonviolent traffickers. But doing so implies neither full legalization nor a corrupt deal with the devil; rather, it is the kind of prioritizing that societies do all the time.

We put more law-enforcement effort into catching murderers than prostitutes; we punish more severely a burglar who kills a homeowner than one who simply steals his prized possessions. Yet, nobody would say the state has a pact with sex workers or turns a blind eye to nonlethal burglary. Indeed, this is how we fight drugs at home: From street corner dealers to wholesale distributors, traffickers know that, whatever their chance of arrest, it will increase dramatically if they kill cops, innocent bystanders, or even rivals.

States only can deter additional wrongdoing by holding force in reserve. Calderon's all-out war "without distinction" may have helped counter accusations of protecting certain kingpins, but it eliminated cartels' incentives to avoid violence. The result? An environment where violence pays, and where the most brutal cartel - Los Zetas - has flourished, becoming the second most powerful in Mexico.

As for U.S. marijuana legalization, its effects on violence in Mexico are easily overstated. Obama has not ruled out federal prosecution of pot production, so Mexican marijuana imports won't stop overnight. Still, as Peña Nieto has said, "it opens a space for a rethinking of our (drug-war) policy." He joins a chorus of Latin American leaders urging a reassessment of a global prohibition regime that has not only failed by its own standards, but brought immense human suffering to the region.

For now, though, prohibition will continue; drugs, guns and money will still crisscross the border; and cartels will compete for the spoils with increasingly fearsome arsenals. In such a world, prioritizing deterrence over drug interdiction makes good sense.

Done right - and we can help to ensure it is - a targeted, conditional approach can reduce violence and corruption in Mexico. It may not stop the flow of drugs, but then neither has filling our prisons with drug offenders. As we contemplate a more realistic and humane drug policy at home, we should facilitate our southern neighbor's efforts to do the same.